Portable unit for metabolic analysis

ABSTRACT

The Portable Unit for Metabolic Analysis measures human metabolic function. The compact invention attaches to the face of a subject and it is able to record highly time-resolved measurements of air temperature and pressure, flow rates during inhalation and exhalation, and oxygen and carbon dioxide partial pressure. The device is capable of ‘breath-by-breath’ analysis and ‘within-breath’ analysis at high temporal resolution.

ORIGIN OF THE INVENTION

The present disclosure is based on work performed by employees of theUnited States Government and may be manufactured and used by or for theGovernment for Government purposes without the payment of any royaltiesthereon or therefore.

The present disclosure is also made in the performance of work under aNASA contract and is subject to the provisions of Section 305 of theNational Aeronautics and Space Act, Public Law 111-314, § 3 (124 Stat.3330, 51 U.S.C. Chapter 201).

FIELD OF INVENTION

The present invention relates to systems for measuring human metabolicfunction and rates. More specifically, the present invention relates toa portable instrumented system that measures inhalation and exhalationairflow rates, heart rate and concentrations of carbon dioxide andoxygen in inhaled and exhaled breath.

BACKGROUND OF THE INVENTION

Measurements of a test subject's breathing rate, oxygen use rate, andproduction of carbon dioxide provide useful physiological data that canbe used to gauge general health as well as the efficiency of the body inthe utilization of dietary energy. Analysis of ventilation and pulmonarygas exchange provides a means for evaluating metabolic function undervarious circumstances of health and in the doing of physical work.Improvements and reduction in the size and weight of gas analyzers andcomputers have resulted in the appearance of a number of automatedventilation and pulmonary gas exchange analyzers. Such devices rangefrom complicated laboratory systems requiring the use of powerfulcomputers to simpler, less versatile systems for clinical use. Notablylacking among the prior art devices for metabolic measurement is thecombination of portability and real-time data collection.

The most commonly measured variables are respiratory volume flow rate,oxygen consumption, carbon dioxide production, heart rate andrespiratory exchange ratio, which is the ratio of carbon dioxideproduced to oxygen consumed.

Earlier efforts directed towards respiratory gas analysis involve thetimed collection of expired breath in rubberized breathing bags,measuring the volume collected, and analyzing the gas compositioncontained within. Metabolic rates were then calculated from the data.Obviously such a method was time consuming, non-portable, error-prone,and able to be performed only by well-equipped laboratories. Moreover,such methods were not suited to the measurement of short durationtransients in metabolic functions.

One prior art solution was to record the relevant analog or digital datain a portable recorder, for later analysis.

At this time, there are four companies that sell portable units for themeasurement of metabolic parameters by means of the analysis of inhaledand exhaled air and heart rate. The four products are:

COSMED of Rome, Italy: Model “K4b2”

Medical Graphics Corp. of St. Paul Minn.: Model “V02000”

SensorMedics Corp of Yorba Linda, California: Model “VmaxST”

Erich JAEGER GmbH of Hochberg, Germany Jaeger-Toennies: Model “OxyconMobile”

Each of these four portable systems employs relatively slowelectrochemical sensor systems for oxygen analysis. Such ‘wet chemistry’systems, in practice, operate at near their limits when driven at ratescorresponding to human inhale/exhale rates. This means that theoxygen-sensor measurements must be corrected due to the relatively slowsensor lag times. The accuracy of these commercially available portableunits is considerably less than large stationary metabolic carts used inhospitals. They also sample and analyze only a small portion of theexhaled air, rather than the entire volume of air that is inhaled andexhaled. Numerous studies were reviewed detailing operation of thesefour portable units compared to metabolic carts; such studies indicatethat these types of commercial portable units typically have variableaccuracy over the range of use, and yet they are considered to providevaluable approximations for field use outside of a clinical setting.

The COSMED model K4b2 appears to be covered by U.S. Pat. No. 4,658,832,to Brugnoli, with an assignment to COSMED, which is an Italian company.This '832 patent describes a portable system comprising a face mask thatis fitted with a flow-measuring turbine and a what is called a “SLOW”analyzer for oxygen concentration of a small portion, approximately 1%,of the exhaled breath. Metabolic activity is calculated on the basis ofcomparison of ambient oxygen concentration to exhaled oxygenconcentration; exhaled carbon dioxide is not measured directly, butrather is inferred in the change in oxygen concentration between inhaledand exhaled air. Moreover, the oxygen concentration of exhaled air isbased on averaging over one or more breaths. The device also uses aturbine to measure, or at least infers the exhaled airflow rate. Theinertia of the turbine has to be taken into account during theend-of-breath phase of exhalation. Temporal resolution of this systemis, at best, on a scale that is not less than that of a singleinhalation/exhalation cycle.

The Medical Graphics model VO2000 seems to be covered by U.S. Pat. No.6,554,776, to Snow, et al., assigned to Medical Graphics, said patentdescribing a portable method for measuring metabolism. This prior artinvention uses a “bi-directional differential pressure Pitot tube”device called a “pneumotach” to measure inhaled and exhaled air-flowrates. The pneumotach device is described specifically in U.S. Pat. No.5,038,773 and No. 5,119,825. The VO2000 product also employs aheart-rate monitor of the sort that utilizes multiple skin-mountedelectrode pickups. The device extracts small gas samples from thepneumotach device, which are then measured for “oxygen uptake and carbondioxide production . . . on a breath-by-breath basis” i.e., on asingle-breath basis, and with, therefore, a single-breath degree oftemporal resolution. The specific means by which oxygen and carbondioxide are measured are not described in this method patent, but thediagrams suggest said means are remote from the test subject's mouth andnose. The anaerobic threshold is calculated on the basis of the averageheart rate.

No specific U.S. Patent could be uncovered for the SensorMedics modelVmaxST. However, U.S. Pat. No. 6,581,595 to Murdock, et al., andassigned to SensorMedics, a U.S. company, shows a simplifiednon-portable system that might utilize oxygen and carbon dioxidemeasurement methods that are similar in principle to those used in theportable VmaxST model. Further information on the VmaxST unit, includingdescriptive information, and a photograph, are athttp://www.summittechnologies.ca/products/metabolics.htm. The modelVmaxST includes a face mask and a radio-transmitting sending unit thatis worn on the body of the test subject. The VmaxST diverts a smallsample of exhaled gas, which is analyzed remotely from the face. Oxygenconcentration is measured with by means of an electro-chemical cell,which has an intrinsic time delay, and CO₂ is measured by means of IRabsorption, also remote from the face of the test subject. The unit hassingle-breath temporal resolution. Heart rate is measured with ECGelectrodes.

No specific U.S. Patent could be uncovered for the fourth portable unitlisted above, the model Oxycon Mobile made by Jaeger-Toennies. However,a manufacturer's brochure, in *.pdf format, is available from VIASYSHealthcare Inc., located at 22745 Savi Ranch Parkway in Yorba Linda,Calif. 92887-4668. The device shown in the brochure comprises a facemask to which a non-turbine type flow-rate measurement deviceincorporates a single tube that carries a portion of the inhaled andexhaled gases to a back-worn analyzer and transmitter having a range of1,000 meters. Heart rate is measured with optional 3- or 12-lead ECGpickups. The methods of gas analysis are not specified, but the brochureimplies that both carbon dioxide and oxygen concentrations are measured,albeit from only a portion of the exhaled gas. The descriptive brochuredoes not mention high data rates, which suggests that the device'stemporal resolution is on the order of a single breathing cycle.

SUMMARY OF THE INVENTION

According to the present invention, there is disclosed a portable unitfor metabolic analysis of a test subject. The portable unit includes amask adapted for covering the test subject's mouth and nose. The maskhas a manifold portion which bifurcates into first and second manifoldflow channels that are open at their free ends and is adapted forconveying inhaled and exhaled air to and from the test subject. A carbondioxide (CO₂) sensor subsystem is disposed in the first manifold flowchannel. An oxygen sensor subsystem is disposed in the first manifoldflow channel. An airflow rate sensor is disposed in the second manifoldflow channel. A computer is connected to the carbon dioxide sensorsubsystem, the oxygen sensor subsystem, and the airflow rate sensor forreceiving data signals from the carbon dioxide sensor subsystem, theoxygen sensor subsystem, and the airflow rate flow sensor and fordigitizing the data signals into digitized data and wirelessly conveyingthe digitized data to another computer which stores the digitized datafor display and analysis.

Also according to the present invention, the carbon dioxide sensorsubsystem has an inner support housing, an intermediate support housingand an outer support housing, and the intermediate support housing formsan air flow channel that is part of the flow manifold through which theair being inhaled and exhaled by the test subject passes.

Further according to the present invention, a plurality of infraredlight-emitting diodes are mounted onto an interior surface of the innersupport housing to project IR energy through the air flowing through theair flow channel of the intermediate support housing.

Still further according to the present invention, a sapphire window isdisposed between the intermediate support housing and the inner supporthousing for separating the infrared light-emitting diodes from the airflow channel. A photo detector is mounted in the outer support housing;and a narrow-band-pass filter is disposed between the outer supporthousing and the intermediate support housing across the airflow channelfrom sapphire window to allow a selected bandwidth of the IR energy fromthe LEDs to pass through to photo detector. Each of the LEDs ispositioned to direct their energy at the photo detector. The LEDs aredriven at about 1.0 to about 2.0 amps and in pulses having a duty cycleof about 0.01 to about 0.1 percent. The photo detector is situated upona thermoelectric cooling device which conveys heat to a heat-dissipatingfin assembly.

Yet further according to the present invention, the oxygen-sensingsubsystem is located in the flow manifold with the CO₂ subsystem. Theoxygen-sensing subsystem has a lower removable housing, an intermediatehousing including an enclosed cylinder which is integral with manifoldflow channel and an upper housing. The oxygen-sensing subsystemincludes: an optic fiber for conveying a blue laser light into the lowerhousing of oxygen sensor; and a collimating optics system for directingthe blue light across the air passing through enclosed cylinder andbeing sampled for oxygen concentration of the air being inhaled andexhaled by the test subject and into a support disk having a layer ofruthenium-based, oxygen-quenched fluorophore dye disposed thereon andmounted in the upper housing. The collimating optics system includes amirror and first, second and third lenses which are held withinremovable housing. Orange light is reflected back to a detector disposedwithin the box by way of the optics system and the optic fiber. The bluelaser light is sinusoidally intensity-modulated at 40 kHz, whereby theresulting orange fluorescence from the excited fluorophore dye layer isphase-shifted relative to incident blue light.

According to the present invention, the oxygen sensor subsystem includesa temperature measuring device located near the oxygen sensitive dyelayer in the upper housing to and connected to the computer to measurethe temperature of the air being inhaled and exhaled by the testsubject. The temperature measuring device is selected from the groupconsisting of a thermocouple and a resistive temperature sensor.

Further according to the present invention, airflow rate sensor is anultrasonic flow sensor that measures the inhalation and exhalation flowrates of the test subject within the one manifold flow channel. Theairflow rate sensor measures a flow rate measurement of about 200 litersper minute in the single manifold flow channel.

Also according to the present invention, a pressure transducer measuresambient air pressure.

Yet further according to the present invention the portable unitincludes a heart-rate monitor adapted to send an output signal to thecomputer.

According to the present invention, a method of making a metabolicanalysis of a test subject, comprises the steps of: covering the testsubject's mouth and nose with a mask having a manifold portion whichbifurcates into first and second manifold flow channels that are open attheir free ends whereby inhaled and exhaled air can be conveyed to andfrom the test subject; measuring the carbon dioxide level of the inhaledand exhaled air being conveyed to and from the test subject with acarbon dioxide sensor subsystem disposed in the first manifold flowchannel; measuring the oxygen level of the inhaled and exhaled air beingconveyed to and from the test subject with an oxygen sensor subsystemdisposed in the first manifold flow channel; measuring the airflow rateof the inhaled and exhaled air being conveyed to and from the testsubject with an airflow rate sensor disposed in the second manifold flowchannel; generating digitized data from data signals received from thecarbon dioxide sensor subsystem, the oxygen sensor subsystem, and theairflow rate sensor and the airflow rate flow sensor; and storing thedigitized data for display and analysis.

Also according to the present invention, the method includes the step ofgenerating digitized data from data signals received from the carbondioxide sensor subsystem, the oxygen sensor subsystem, and the airflowrate sensor and the airflow rate flow sensor in a first computer carriedby the test subject. The method also includes the step of wirelesslyconveying the digitized data to a second computer which stores thedigitized data for display and analysis.

According to the present invention, a carbon dioxide sensor for sensingthe level of carbon dioxide in air being inhaled and exhaled by a testsubject, comprises: an inner support housing; an outer support housing;an intermediate support housing forming an air flow channel throughwhich the air being inhaled and exhaled by the test subject passes; anda plurality infrared light-emitting diodes being mounted onto aninterior surface of the inner support housing to project IR energythrough the air flowing through the air flow channel of the intermediatesupport housing. A sapphire window is disposed between the intermediatesupport housing and the inner support housing for separating theinfrared (IR) light-emitting diodes from the air flow channel. A photodetector is mounted in the outer support housing and a narrow-band-passfilter is disposed between the outer support housing and theintermediate support housing across the airflow channel from sapphirewindow to allow a selected bandwidth of the IR energy from LEDs to passthrough to photo detector. The photo detector is situated upon athermoelectric cooling device which conveys heat to a heat-dissipatingfin assembly. Each of the LEDs positioned such that they all aimed todirect their light at the photo detector. The LEDs are driven at about1.0 to about 2.0 amps and in pulses having a duty cycle of about 0.01 toabout 0.1 percent.

Further according to the present invention, an oxygen-sensing subsystemfor sensing the level of oxygen concentration in air being inhaled andexhaled by a test subject, comprises a lower removable housing; anintermediate housing including an enclosed cylinder forming an air flowchannel through which the air being inhaled and exhaled by the testsubject passes; an upper housing; an optic fiber for conveying a bluelaser light into the lower housing of oxygen sensor; and a collimatingoptics system for directing the blue light across the air passingthrough enclosed cylinder and into a support disk having a layer ofruthenium-based, oxygen-quenched fluorophore dye disposed thereon andmounted in the upper housing. The collimating optics system includes amirror and first, second, and third lenses which are held withinremovable housing. A photo detector is provided to which orange lightreflects back to by way of the optics system and the optic fiber. Theblue laser light is sinusoidally intensity-modulated at 40 kHz, wherebythe resulting orange fluorescence from the excited fluorophore dye layeris phase-shifted relative to incident blue light.

A temperature measuring device is located near the oxygen sensitive dyelayer in the upper housing to measure the temperature of the air beinginhaled and exhaled by the test subject. The temperature measuringdevice is selected from the group consisting of a thermocouple and aresistive temperature sensor.

BRIEF SUMMARY OF THE DRAWINGS

The structure, operation, and advantages of the present invention willbecome further apparent upon consideration of the following descriptiontaken in conjunction with the accompanying figures (Figs.). The figuresare intended to be illustrative, not limiting.

Certain elements in some of the figures may be omitted, or illustratednot-to-scale, for illustrative clarity. The cross-sectional views may bein the form of “slices”, or “near-sighted” cross-sectional views,omitting certain background lines which would otherwise be visible in a“true” cross-sectional view, for illustrative clarity.

In the drawings accompanying the description that follows, often bothreference numerals and flow channel ends (labels, text descriptions) maybe used to identify elements. If flow channel ends are provided, theyare intended merely as an aid to the reader, and should not in any waybe interpreted as limiting.

FIG. 1 is a front isometric view of the present invention;

FIG. 1A is a top view of the essential element

FIG. 2 is a schematic cross-sectional view of thecarbon-dioxide-concentration measuring subsystem portion of the presentinvention;

FIG. 3 is a schematic cross-sectional view of the oxygen-concentrationmeasuring subsystem portion of the present invention;

FIG. 4 is a representation of metabolic data taken from a human testsubject;

FIG. 5 is a schematic view of the oxygen-concentration measuringsubsystem portion typically disposed in the electronics box of thepresent invention;

FIG. 6 is a schematic view of the optical filtering system portion ofthe oxygen-concentration measuring subsystem of FIG. 5; and

FIG. 7 is a schematic view of an alternative embodiment of anoxygen-concentration measuring subsystem portion typically disposed inthe electronics box of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a representational frontal isometric view of a Portable Unitfor Metabolic Analysis (a.k.a. PUMA) 10 adapted to be attached to theface of a human test subject. The PUMA unit 10 comprises a standard facemask 14 of the sort that is adapted to cover the test subject's mouthand nose. While the mask is illustrated as completely covering the testsubjects mouth and nose, it is also within the terms of the invention tosimply use a mouthpiece and nose clip. The nose clip eliminatesbreathing through nose and directs all inhale/exhale flow from the mouthto PUMA 10. Within the terms of the present application, the face mask14 includes either the mask as shown or a mouthpiece and nose clip. Themask 14 has a manifold portion 16 which bifurcates into two flowchannels 16L and 16R, which convey inhaled and exhaled air to and fromthe test subject 12.

As shown in FIGS. 1 and 1A, flow channel 16L contains a conduit with acarbon dioxide (CO₂) sensor subsystem 50 and an oxygen (O₂) sensorsubsystem 70. Flow channel 16R has a conduit with an ultrasonic flowsensor 22 which includes two transducers 22′ and 22″. Wires 24 from thetransducers 22′ and 22″ lead to a larger cable 26 that communicates witha small digitizing and transmitting computer (not shown) disposed withinelectronics box-like structure 30. The large cable 26, with plug 27 atits distal end, plugs into a port 27′ of the box-like structure 30 andthereby communicates with the digitizing computer, conveying datathereto from the aforementioned sensors for oxygen, carbon dioxide, andairflow rate. NOTE: A fiber optic line 76 is contained within the cablebundle 26 and has a terminal connector 31 which connects with the socket31′ on the box 30 that also contains the digitizing computer. A bluelaser light, as explained below, causes a dye inside of the oxygensensor 70 to fluoresce in a color different from blue, such as orange.The fluorescent light is also conveyed through the same optic fiber 76from the oxygen sensor 70 to the box 30 that contains a means to measurethe oxygen-proportional phase shift (relative to the blue laser light)of the light that has been excited to fluorescence by the blue laserlight that travels in the optic fiber. Heart rate is measured separatelyby means of a heart-rate monitoring band (not shown) that is worn aroundthe chest of the test subject. The heart rate sensor can be a wirelessheart rate sensor with a receiver mounted adjacent to the flow sensor(22). For example, the heart rate receiver can be made by Polar Corp.The heart-rate data is also fed into the digitizing computer by means ofthe cable 26 with plug 27 and socket 27′. The small box 30 is carriedupon the person of the test subject when the PUMA invention is beingused. The computer digitizes the data signals from the aforesaid sensorsand wirelessly conveys the digitized data to a desktop or laptopcomputer (not shown) which in turn stores the digitized data for displayand analysis. In addition to the raw data (air temperatures, pressure,flow, oxygen and carbon dioxide mole fraction, heart rate), theinventors intend that the computer display will further include (but notbe limited to) volumetric oxygen consumption, volumetric carbon dioxideproduction, respiratory equivalent ratio and volumetric flow rate ofexhaled gas.

Referring to FIG. 1A, as the test subject breathes in and out, air movesin both directions, as shown by the arrows, within flow channels 16L,16R of the manifold 16 of the mask 14. The flow sensor 22 in the flowchannel 16R measures the airflow speed, and thus air flow rate duringinhalations and exhalations, in the flow channel 16R only. Flowimpedance of each flow channel 16,16R is constant, so that the airflowsensor 22 in the flow channel 16R is able to measure an airflow ratethat can be calibrated so as, effectively, to determine for the sum ofthe inhalation and exhalation flow rates in both manifold flow channels.

The metabolic parameters of specific interest are air pressure andtemperature, inhaled and exhaled airflow rates, heart rate, and thepartial pressures of inhaled and exhaled oxygen and carbon dioxide.

Commercial, off-the-shelf technology that is described in more detailhereinbelow is used to measure air pressure and temperature, and airflowrate. Measurements of the partial pressures of inhaled and exhaledoxygen and carbon dioxide are done by means of hardware developed at theNASA Glenn Research Center. Each measurement subsystem of the presentinvention is described in detail below.

Carbon Dioxide Measurement Subsystem

FIG. 2 is a schematic, cross-sectional top view of the carbon dioxidesensor subsystem 50 through line 2-2 of FIG. 1, showing the air flowchannel 51, within the flow channel 16L, as perpendicular to, or cominginto and out of the page of FIG. 2. Sensor 50 has an inner supporthousing 60, an intermediate support housing 62 and an outer supporthousing 61. The intermediate support housing 62 forms the air flowchannel 51 and is part of the flow manifold 16L. The inner supporthousing 60 has a curved interior surface 60 a formed between upright endwall 60 b which in turn forms a collar 60 c.

A plurality infrared (IR), light-emitting diodes (LEDs) 52 are mountedonto the curved interior surface 60 a to project IR energy through theair flowing through the air flow channel 51 of intermediate supporthousing 62. Although an array of eight infrared (IR) light-emittingdiodes (LEDs) 52 are shown, it is within the scope of the presentinvention to use any desired number of LEDs. A plurality of individualLEDs 52 (made by Ioffe in St. Petersburg, Russia) are used inconstructing the exemplary array of LEDs 52 as shown. The intermediatesupport housing 62 has an inner end 62 a that is secured against theupright end wall 60 b and the collar 60 c of the inner support housing60. A sapphire window 54 is mounted between the inner end 62 a of theintermediate support housing 62 and the upright end wall 60 b of theinner support housing 60. A gasket 59 a disposed between intermediatesupport housing 62 and inner support housing 60 maintains the IRsapphire window 54 in place. The sapphire window 54 separates theinfrared (IR) light-emitting diodes (LEDs) 52 mounted onto the curvedinterior surface 60 a from the air flow channel 51 and isolates the LEDsfrom humidity and moisture in the inhaled and exhaled gas, i.e. theusers breath.

The sapphire window 54 can have an anti-fog coating applied the surfacewithin airflow channel 51 to eliminate the effects of condensationduring exhalation.

The IR energy, after passing through sapphire window 54 propagatesthrough the airflow channel 51 to a narrow-band-pass filter 55 mountedbetween the outer support housing 61 and the intermediate supporthousing 62 across the airflow channel 51 from sapphire window 54. Agasket 59 b disposed between intermediate support housing 62 and outersupport housing 60 maintains filter 55 in place. The narrow-band-passfilter 55 allows a selected bandwidth of the IR energy from LEDs 52.i.e., 4.25 to 4.44 microns to pass through to a photo detector 56mounted in the outer support housing 61. The photo detector 56 issituated upon a thermoelectric cooling device 57 which conveys heat to aheat-dissipating fin assembly 58.

The LEDs 52 of the array are positioned such that they all aimed todirect their light at the detector 56. For example, LEDs 52 are arrangedsuch that seven of the LEDs are arranged in a circle around a singlecentral LED. Each LED has a lens to collimate its output. Each of theeight LEDs 52 are rated at greater than 120 microwatts peak when drivenat 1 amp, but in this invention they are driven at about 1.0 to about2.0 amps and preferably about 1.3 to about 1.6 amps and most preferablyabout 1.5 amps and in pulses having a duty cycle of about 0.01 to about0.1 percent and preferably about 0.02 to about 0.06 percent and mostpreferably about 0.04 percent. If the LEDs 52 are driven at more thanabout 0.1 percent, then the life of the LEDs will be significantlyreduced. If the LEDs 52 are driven at less than 1.0 amps then theintensity of the IR energy will not be sufficient to be measuredaccurately by the photo detector (56). If the LED pulse width is lessthan 10 μsec, the pulsing circuitry powering the LEDs will haveinsufficient time to provide a stable output to the LEDs. Accordingly,if the pulse width is shorter than 10 μsec, the Infrared energy from theLEDs will not be constant and the accuracy of the measurement willdecrease. The on-board microprocessor acquires the electrical signalfrom detector 56 approximately 10 μsec after the ON pulse is sent to theLED array to allow the pulsing circuitry powering the LEDs to stabilize.

The filter 55 has its peak transmission at 4.350 microns and has a fullwidth, half max of 0.18 microns. Power cable 53 conveys power to the IRLED array 52 that is mounted within the housing 60. Wire 64 conveysvoltages from photo detector 56 into the cable 66 which also carriespower, of about 0.25 watts, to the thermoelectric cooling device 57. Anexemplary detector 56 is a passive photovoltaic Mercury CadmiumTelluride (HgCdTe) detector manufactured by Judson Technologies. Thethermoelectric cooling device 57 serves the dual purpose of stabilizingthe response of the detector 56 and increasing its sensitivity.

Measurements of the carbon dioxide partial-pressures are achieved bymeans of a relatively sharp IR absorption line for carbon dioxide at awavelength of about 4.2 to about 4.5 microns and preferably about 4.3microns. The wavelength is chosen because it is unaffected by variationsin the concentration of water vapor in the air stream that moves withinthe flow channel 51 of manifold flow channel 16L. Relatively broad-bandIR energy from LEDs 52 traverses the filter 55 before striking the IRsensor 56. The inhale/exhale airstream passes between the IR source 52within the housing 60 and the HgCdTe photo detector 56, thus attenuatingthe 4.3 micron (urn) portion of the IR energy from the LED array 52.

The CO₂ subsystem 50 uses the absorption feature located at the 4.3 umwavelength. The LEDs 52 are pulsed at about 5 to about 15 Hz andpreferably at about 10 Hz and at a low duty cycle so as to minimize theamount of heat that is conveyed to the detector 56.

The main reason for pulsing LEDs 52 is to minimize the heat buildup inthe LEDs and prolong their lives. However if the LEDs 52 were oncontinuously, they would heat up the detector 56. The ON duty cycle isabout 0.01 to about 0.1 percent and preferably about 0.02 to about 0.06percent and most preferably about 10 percent of the complete ON pulse ofthe LEDs 52. (What? Translation please; maybe this sentence should bedeleted.)

Oxygen Measurement Subsystem

FIG. 3 is a cross-sectional, schematic side view of the oxygen-sensingsubsystem 70 located in the flow manifold 16L, preferably upstream fromthe CO₂ subsystem 50. The subsystem 70 has a lower housing 77, anintermediate housing 81 and an upper housing 86.

During inhalation and exhalation of a test subject, air flowsbidirectionally, according to the double-headed arrows 71, within theenclosed cylinder 72 of intermediate housing 81, which is integral withmanifold flow channel 16L of FIG. 1.

The oxygen partial pressure measurement subsystem 70 utilizes thefluorescence oxygen-quenching properties of a Ruthenium-doped organicdye, such as tris (4,7-diphenyl-1,10-phenanthroline) ruthenium (II)perchlorate, as describe by Bacon, et al., in U.S. Pat. No. 5,030,420.The excitation source is a blue laser diode (not shown), the blue light74 of which is conveyed into the lower housing 77 of oxygen sensor 70 byway of an optic fiber 76. The blue light 74 traverses the collimatingoptics set which includes mirror 77 d and lenses 77 a, 77 b, and 77 cand are held within removable housing 77. After the blue light istransmitted through lens 77 a, it crosses the air held in cylinder 72and is directed into a thin support disk 78 mounted in the upper housing81.

A thin layer 79 of ruthenium-based, oxygen-quenched fluorophore dye isdisposed upon the flat, thin support sensing disk 78, across which theair being sampled for oxygen concentration passes during theinhalation/exhalation of the test subject. Orange fluorescent light(excited by the blue laser light) of the ruthenium-based fluorophore dyelayer 79 is “quenched” to a degree that is directly related to theconcentration of oxygen that comes into contact with the dye layer. Theorange light 80 reflects back to a oxygen measurement subsystem 500 byway of the same optics system 77 d, 77 c, 77 b, and 77 a to optic fiber76 as is used by the incoming blue laser light 74. The oxygenmeasurement subsystem 500, shown in FIGS. 5 and 6, is shown inincorporated in the box 30 that holds the digitizing computer. Theoxygen-concentration measuring detector system 500 (see FIGS. 5, 6, and7) which measures the intensity of the orange light 80, and its phaseshift relative to the blue light, is contained within the same box 30that holds the digitizing computer. That is to say, the fiber optic line76 conveys blue light from a laser diode source that is disposed withinthe box 30 (see FIG. 1) to the oxygen sensor subsystem 70. The fiberoptic line 76 also conveys the return light signal of what is shown hereas orange light 80 back to a photo detector 502 that is also disposedwithin the detector system 500 provided in electronics box 30.

The fluorophore dye is the basis of a commercial product that measuresgaseous and dissolved oxygen concentrations within a fluid (liquid orgas). When excited to fluorescence by blue light, the specific dye usedby the inventors thus far fluoresces orange light. Oxygen quenches thefluorescence process to a degree is related to the concentration ofoxygen that makes contact with the dye layer 79. The oxygen subsystem 70uses Ocean Optics probe tips 79, but operates in a manner that has beenmodified from that supplied by Ocean Optics. The laser diode (not shown,though disposed within the box 30 in FIG. 1) is sinusoidallyintensity-modulated at 40 kHz. The resulting orange fluorescence fromthe excited fluorophore dye layer 79 is phase-shifted relative to theincident blue light.

The oxygen sensor subsystem 70 also includes a thermocouple or resistivetemperature sensor 82 in the upper housing whose voltage is conveyed tothe computer 30 by way of electrical lead 84 which is secured within thesupport housing 86. (Jeff, there is a voltage reference that provides aconstant voltage to the resistive temperature sensor connected to avoltage divider network. The microprocessor measures the voltage acrossthe divider network to determine the temperature.) The electrical lead84 from the resistive temperature sensor 82 is connected to cable 87,which conveys the resistance of the resistive temperature sensor to themain cable 26 (FIG. 1). The resistive temperature sensor 82 measures thetemperature of the air being inhaled and exhaled. Temperaturemeasurement by means of the resistive temperature sensor 82 is acritical element to the calibration of the oxygen sensor 70, which iswhy the resistive temperature sensor 82 is located close to the oxygensensitive dye layer 79 on the thin surface 78. An exemplary resistivetemperature sensor 82 is made by Thermometrics. However it is within thescope of the invention for the element 82 to be a thermocouple.

Referring to FIGS. 5 and 6, there is illustrated a schematic view of theoxygen-concentration measuring subsystem portion 500 typically disposedin the electronics box 30 of the present invention. Theoxygen-concentration measuring subsystem portion 500 is secured to oneend of the multimode optical fiber 76 by an optic connector box 510. Ablue light 74 from a blue light source laser diode 504 is directedthrough a multimode optical fiber 76 a through a lens 514, onto anoptical filtering system 508, then through a lens 516, into themultimode optical fiber 76 b, into multimode optical fiber 76, acrossthe collimating optics set, through the air in cylinder 72 and onto thesensing disk 78.

The sensing disc 78 then fluoresces and the light propagates backthrough the fiber 76, through a lens 516 and through an optical filter508. The optical filter 508 removes any remaining blue light from theorange light before going through a lens 512, a optical fiber 76 c andto a photo detector 502. Finally the orange light reaches a photodetector 502. The signal received at the photo detector 502 is comparedto the signal used to drive the laser diode 504.

FIG. 6 is a schematic view of the optical filtering system portion ofthe oxygen-concentration measuring subsystem of FIG. 5. During operationof the oxygen sensor subsystem 70, the PUMA electronics system withinbox 30 measures the phase-shift between the incident blue 74 andfluorescence orange 80 signals. The electronics and optics of the oxygensensor subsystem 70 work as follows. A 40 kHz signal is generated andfed to a laser diode driver. The laser diode driver in turn drives theblue laser diode, 504, at 40 kHz. The light from the blue laser diode504 propagates through a multimode optical fiber 76 a through a lens 514then reflects off an optical filter 508 and through lens 516, thenthrough the multimode optical fiber 76 b, into multimode optical fiber76, across the collimating optics set, through the air in cylinder 72and onto the sensing disk 78. The sensing disc 78 then fluoresces andthe light propagates hack through the fiber 76, through a lens 516 andthrough an optical filter 508. The optical filter 508 removes anyremaining blue light from the orange light before going through a lens512, a optical fiber 76 c and to a photo detector 502. The signalreceived at the photo detector 502 is compared to the signal used todrive the laser diode 504. The phase shift between these two signals iswhat is correlated to any oxygen concentration. The degree ofphase-shift correlates with the oxygen partial pressure within the flowof gas in the duct 72. In order to minimize photo-bleaching of thefluorophore, the PUMA unit is designed to gate the blue laser diode at10 Hz, with about a 10% duty cycle.

Referring to FIG. 7, there is shown a schematic view of an alternativedesign of an oxygen-concentration measuring subsystem portion 700typically disposed in the electronics box 30 of the present invention.The alternate electronics and optics of the alternateoxygen-concentration sensor subsystem 700 work as follows. A 40 kHzsignal is generated and fed to a laser diode driver. The laser diodedriver in turn drives the blue laser diode, 504, at 40 kHz. The bluelaser light 74 propagates through multimode optical fiber 76 d thenthrough multimode optical coupler 700. The blue laser light exitsmultimode coupler 700 at port 700 a and propagates through multimodeoptical fiber 76 b, then into multimode optical fiber 76, across thecollimating optics set, through the air in cylinder 72 and onto thesensing disk 78. The sensing disc 78 then fluoresces and the lightpropagates back through the fiber 76 and 76 b, to port 700 a ofmultimode optical coupler 700. The fluorescence exits multimode coupler700 at port 700 c and 700 d. The light at 700 c is ignored. The lightexiting port 700 b propagates though multimode optical fiber 76 e tooptical filter 701 where any remaining blue laser diode light isremoved. The fluorescence light then propagates through optical fiber 76f to a photo detector 502. As in the embodiment shown in FIGS. 5 and 6,the signal received at the photodiode is compared to the signal used todrive the blue light source laser diode. The phase shift between thesetwo signals is what is correlated to the partial pressure of oxygen atthe probe tip 78.

Airflow Measurement Subsystem

The airflow rate sensor 22 (FIG. 1) of the invention 10 is a modifiedversion of a commercial ultrasonic flow sensor manufactured by GillInstruments Limited, in Lymington, England. The flow sensor 22 measuresinhalation and exhalation flow rates within the one manifold flowchannel 16R shown in FIG. 1 but, as described below, suffices to measurethe airflow rate in both flow channels 16L,16R of the manifold 16. Theair-flow rate measurement device 22 is able to measure total flow ratesof up to 400 liters per minute, as inferred for both manifold flowchannels 16L, 16R, instead of the design maximum flow-rate measurementof 150 liters per minute.

Part of the increased flow rate measurement derives from the bifurcatednature of the manifold 16 (FIGS. 1 and 1A) whereby the constant flowimpedance of each manifold 16L and 16R enables the flow measurement ofone manifold (16R in FIGS. 1 AND 1A) to be used as a basis for inferringthe total flow of both manifold portions 16,16R. Note that the flowsplit between manifold portions 16,16R need not be equal. The impedancejust needs to be constant so the total flow can be deduced or measuredfrom the flow measurement. Part of the modification of the original Gillinstrument entails a recalibration of the output variables from thetransducers 22′, 22″, so as to allow a flow rate measurement ofapproximately 200 liters per minute in the single manifold flow channel16R, and a 400-liter-per-minute total flow rate to be inferred for bothflow channels 16L, 16R of the system 10. Another modification from theoriginal Gill instrument design is that the signals from the transducers22′, 22″ are calibrated within the digitizing computer contained in box30 (FIG. 1), rather than within a unitary transducer plug-in device thatis supplied as part of the original Gill instrument package.

The Gill ultrasonic flow velocity device 22 acquires data at a rate of10 Hz.

Pressure and Temperature

The PUMA invention 10 uses a commercial, off-the-shelf (COTS) miniaturediaphragm-type pressure transducer to measure ambient air pressurewhich, though originally housed within the manifold portion 16 or one ofthe flow channels 16L,16R thereof, is housed within the box 30 thatholds the digitizing computer. Human testing of the invention has shownthat pressure within the manifold flow channels 16L, 16R variesminimally during inhalation and exhalation, and that, therefore, thepressure transducer needs only to provide a measure of the ambient airpressure.

Heart Rate Monitor Subsystem

The PUMA unit uses a COTS heart-rate monitor, such as a heart-ratemonitor made by Polar Corp. The receiver for the heart rate sensor islocated adjacent to the flow sensor (22). It is unmodified, except thatits output signal is integrated with the PUMA electronics located in thecomputer box 30. The Polar transmitter is of the chest strap type. Theheart rate data is supplied to the computer 30 in the form of a pulseevery heart beat. The heart rate receiver hoard outputs a digital pulseevery time it detects a heart beat. The PUMA acquisition and controlelectronics system located in box 30 then computes a heart rate from thecounts (pulses) that it outputs wirelessly to the external computer at10 Hz (along with the other data).

Acquisition and Control Electronics

The digitizing computer, and the acquisition and control electronics inhousing box 30 of the present PUMA invention, are electronically andoptically tethered to the sensor electronics and optics located on themask 14 by means of the cable 26 and optic fiber 76 shown in FIG. 1. Thecomputer is battery powered and capable of being worn during exercise.The battery for powering the system can be a 7.2-volt, lithium-ion Canoncamcorder battery having a 3,000 mA-hour capacity. The computer containsall of the electronics necessary to control all of the PUMA sensorsdescribed herein above. It digitizes all of the signals from the sensorsand acquires sensor data at 10 Hz. In order to do this, the electronicpackage digitizes the signals from the O₂ and CO₂ subsystems at a muchhigher rate in order to extract the partial pressure information. Thesoftware for the acquisition and control computer is custom-developed inC++.

The computer shares the same housing box 30 as contains the blue laserdiode and other optics features and light-intensity measurement systemsand devices associated with the oxygen measurement system 70 (FIG. 3).

The computer also includes a transmitter and receiver (not shown) so asto communicate wirelessly with a stationary computer (not shown) whichreceives the raw signal data from the PUMA system 10 (serial data streamof temperature in volts, pressure in volts, flow in volts, heart rate inbeats, CO₂ in volts and O₂ in degrees of phase shift) and applies therelevant calibrations to each signal to get actual temperature,pressure, flow, and oxygen and carbon dioxide partial pressures.Software in the stationary computer then calculates such relevantmetabolic data as ventilatory equivalent, volumetric consumption ofoxygen, volumetric production of carbon dioxide, and heart rate, whileall of other metabolic quantities can be derived from thesemeasurements. The software for the stationary external computer isessentially a set of routines that are based on a commercially-availablesoftware package from Wavemetrics, Inc. (IGOR Pro,http://www.wavemetrics.com).

Operation of PUMA

The results of tests on a human subject are shown in FIG. 4, wherein thevolumetric flowrate (V, in liters/minute), and partial pressures ofoxygen (PP₀₂) and carbon dioxide (PP_(C02)) are shown as functions oftime. The times representing the beginning of an inhalation (t_(bi)),beginning of an exhalation (t_(be)) and end of an exhalation (t_(ee))are indicated.

Whereas other systems for measuring human metabolism and metabolic ratesuse gas-analysis and other sensors that are remote from the testsubject, and are often not portable, the PUMA system according to thepresent invention makes all measurements simultaneously and close to themouth at 10 Hz.

FIG. 4 is a display of data taken by means of the PUMA system from anactual human test subject. PUMA measures the ventilatory equivalent(V_(e), Eq. 1 below), production rate of carbon dioxide (V_(C02), Eq. 2)and consumption rate of oxygen (V₀₂ Eq. 3) by numerically integratingthe data in FIG. 4 over an inhale/exhale cycle.

${\overset{.}{V}}_{e} = \frac{\int_{t_{be}}^{t_{ee}}{{\overset{.}{V}(t)}\ d\; t}}{\left( {t_{ee} - t_{bi}} \right)}$${\overset{.}{V}}_{{CO}_{2}} = \frac{\left\lbrack {\int_{t_{be}}^{t_{ee}}{{\overset{.}{V}(t)}X_{{CO}_{2}}\ d\; t}} \right\rbrack - \left\lbrack {\int_{t_{bi}}^{t_{be}}{{\overset{.}{V}(t)}X_{{CO}_{2}}\ d\; t}} \right\rbrack}{\left( {t_{ee} - t_{bi}} \right)}$${\overset{.}{V}}_{O_{2}} = \frac{\left\lbrack {\int_{t_{bi}}^{t_{be}}{{\overset{.}{V}(t)}X_{O_{2}}\ d\; t}} \right\rbrack - \left\lbrack {\int_{t_{be}}^{t_{ee}}{{\overset{.}{V}(t)}X_{O_{2}}\ d\; t}} \right\rbrack}{\left( {t_{ee} - t_{bi}} \right)}$where X_(i) is the mole fraction of species i and is equal to thepartial pressure of species i divided by the total pressure.

Note that inhaled X_(CO2) is normally 0.0 and the inhaled X_(O2) isnormally 0.21.

The primary innovation PUMA offers, compared to prior art portabledevices, is that all gas measurements are made close to the mouth and ata sample rate much greater than other units. All commercial metaboliccarts and fixed units measure gas concentrations remotely from themouth, which allows measurement errors to accumulate. More specifically,the gas from the inhale/exhale streams is sampled and measured atdistances ranging from 3 to 10 ft (and beyond), which introduces thepotential for gas dilution, and for the introduction of timing andsampling issues that have to be addressed in the analysis of the data.Further, all commercial carts and fixed units make one measurement ofoxygen and carbon dioxide, and they assume that concentration isrepresentative of entire single breaths, which misrepresents thepotential that is achieved with the present invention, wherein theclose-to-the-mouth feature minimizes or eliminates the timing issuespresent in other portable and fixed commercial units.

Thus the present invention provides highly time-resolved measurements ofhuman metabolic activity. The present invention further makes use ofunique hardware and software for the measurement of oxygen partialpressure.

Although the invention has been illustrated and described in detail inthe drawings and foregoing description, the same is to be considered asillustrative and not restrictive in character—it being understood thatonly preferred embodiments have been shown and described, and that allchanges and modifications that come within the spirit of the inventionare desired to be protected. Undoubtedly, many other “variations” on the“themes” set forth hereinabove will occur to one having ordinary skillin the art to which the present invention most nearly pertains, and suchvariations are intended to be within the scope of the invention, asdisclosed herein.

The invention claimed is:
 1. A portable unit for metabolic analysis of atest subject, comprising: a device configured to close the testsubject's nose and allow the test subject to only breath through themouth; a first pipe in air flow communication with the mouth of the testsubject; a first manifold portion and a second manifold portion bothextending and both bifurcating from the first pipe; a firstbi-directional air flow path within the first pipe comprising inhalationair flow towards the mouth of the test subject and exhalation air flowfrom the mouth of the test subject; a second and third bi-directionalair flow path within the first and second manifold portions,respectively; wherein during exhalation of the test subject, exhaust airtravels from the mouth of the test subject unidiretionally through thefirst pipe along the first bi-directional air flow path and isbifurcated and travels unidirectionally through the first and secondmanifold portions along the second and third bi-directional air flowpaths; wherein during inhalation of the test subject, inhalation airtravels towards the mouth of the test subject unidiretionally throughthe first and second manifold portions along the second and thirdbi-directional air flow paths and combines to flow unidirectionallythrough the first pipe along the first bi-directional air flow path; acarbon dioxide sensor subsystem disposed in the first manifold portion;an oxygen sensor subsystem disposed in the first manifold portion; anairflow rate sensor disposed in the second manifold portion; and acomputer connected to the carbon dioxide sensor subsystem, the oxygensensor subsystem, and the airflow rate sensor for receiving data signalsfrom the carbon dioxide sensor subsystem, the oxygen sensor subsystem,and the airflow rate flow sensor and for digitizing the data signals andwirelessly conveying the digitized data to another computer which storesthe digitized data for display and analysis.
 2. The portable unit ofclaim 1 wherein the carbon dioxide sensor subsystem has an inner supporthousing, an intermediate support housing and an outer support housing,and the intermediate support housing forms an air flow channel that isconnected to the first manifold portion through which the air beinginhaled and exhaled by the test subject passes.
 3. The portable unit ofclaim 2 wherein a plurality of infrared light-emitting diodes aremounted onto an interior surface of the inner support housing to projectIR energy through the air flowing through the air flow channel of theintermediate support housing.
 4. The portable unit of claim 3 wherein asapphire window is disposed between the intermediate support housing andthe inner support housing for separating the infrared light-emittingdiodes from the air flow channel.
 5. The portable unit of claim 4wherein: a photo detector is mounted in the outer support housing; and anarrow-band-pass filter is disposed between the outer support housingand the intermediate support housing across the airflow channel fromsapphire window allows a selected bandwidth of the IR energy from LEDsto pass through to photo detector.
 6. The portable unit of claim 5wherein the photo detector is situated upon a thermoelectric coolingdevice which conveys heat to a heat-dissipating fin assembly.
 7. Theportable unit of claim 5 wherein each of the LEDs is positioned suchthat each is aimed to direct their light at the photo detector.
 8. Theportable unit of claim 7 wherein the LEDs are driven at about 1.0 toabout 2.0 amps and in pulses having a duty cycle of about 0.01 to about0.1 percent.
 9. The portable unit of claim 1 wherein the oxygen-sensingsubsystem is located in the first manifold portion with the carbondioxide subsystem.
 10. The portable unit of claim 9 wherein theoxygen-sensing subsystem has a lower removable housing, an intermediatehousing including an enclosed cylinder which is integral with the firstmanifold portion and an upper housing.
 11. The portable unit of claim 10wherein the oxygen-sensing subsystem includes: an optic fiber forconveying a blue laser light into the lower removable housing of theoxygen-sensing subsystem; and a collimating optics system for directingthe blue light across the air passing through enclosed cylinder andbeing sampled for oxygen concentration of the air being inhaled andexhaled by the test subject and into a thin support disk having a layerof ruthenium-based, oxygen-quenched fluorophore dye disposed thereon andmounted in the upper housing.
 12. The portable unit of claim 11 whereinthe collimating optics system includes a mirror and first, second, andthird lenses which are held within lower removable housing.
 13. Theportable unit of claim 12 wherein orange fluorescence reflects back to adetector by way of the optics system and the optic fiber.
 14. Theportable unit of claim 13 wherein the blue laser light is sinusoidallyintensity-modulated at 40 kHz, whereby the resulting orange fluorescencefrom the excited fluorophore dye layer is phase-shifted relative toincident blue light.
 15. The portable unit of claim 14 wherein theoxygen sensing subsystem includes a temperature measuring device locatednear the oxygen sensitive dye layer in the upper housing and connectedto the computer to measure the temperature of the air being inhaled andexhaled by the test subject.
 16. The portable unit of claim 15 whereinthe temperature measuring device is selected from the group consistingof a thermocouple and a resistive temperature sensor.
 17. The portableunit of claim 9 wherein the airflow rate sensor is an ultrasonic flowsensor that measures the inhalation and exhalation flow rates of thetest subject within the second pipe.
 18. The portable unit of claim 17wherein the airflow rate sensor measures a flow rate measurement ofabout 200 liters per minute in the second pipe.
 19. The portable unit ofclaim 17 further including a pressure transducer to measure ambient airpressure.
 20. The portable unit of claim 19 further including aheart-rate monitor adapted to send an output signal to the computer.